1. Field of the Invention
The present invention relates generally to a poppet valve for an internal combustion engine, and more particularly to a lightweight engine poppet valve constructed with a mechanically locking interfitting joint connecting the valve head to the valve stem capable of operating at high temperatures and in a corrosive environment.
2. Description of the Related Art
It is well known in the industry that engine poppet valves operate at relatively high temperatures and in corrosive environments. It is further known that exhaust valves operate under more severe conditions than intake valves. The exhaust valves used in diesel and leaded fuel applications, which are considered heavy duty applications, operate in more severe conditions than in other types of internal combustion engines. Engine poppet valves must be able to withstand even the most severe of these conditions and still be durable.
Efforts are constantly being made to improve the construction, design, and manufacturing techniques of engine poppet valves. These efforts include, but are not limited to, making the valve lighter in weight, more economical to manufacture, and more durable. Lighter poppet valves can offer better fuel economy for a vehicle due to weight considerations, and can be manufactured more cost effectively due to less material employed in the valve. In addition, engine poppet valves can be designed with specific chemical and mechanical properties in mind to withstand the harsh temperature and environmental conditions to which engine poppet valves are subjected. Some of these desired chemical and mechanical properties include, but are not limited to, excellent sulfidation resistance, good hot hardness, sufficient oxidation resistance, optimum thermal resistance, and low thermal expansion.
The term xe2x80x9clightweightxe2x80x9d as employed herein is intended to refer to the physical characteristics of the engine poppet valve and its components that make the engine poppet valve light in weight. The term xe2x80x9clightweightxe2x80x9d is also meant to include but not be limited to an ultralight engine poppet valve as that term is defined in U.S. Pat. No. 5,413,073 which is owned by the assignee of the present invention and is hereby incorporated by reference. The assignee of the present invention also owns U.S. Pat. Nos. 5,453,314 and 6,263,849, which are both hereby incorporated by reference.
There is still a desire to make improvements in the manufacturing technique and design of a lightweight engine poppet valve. The engine poppet valve would be constructed in an arrangement that mechanically attaches the valve head to the hollow stem portion in a locking arrangement. Even with this mechanically locking attachment being located in the high temperature and corrosive combustion zone, the lightweight poppet valve would provide excellent sulfidation resistance, good hot hardness, good oxidation resistance, and optimum thermal conductivity with low thermal expansion, optimum thermal resistance, and durability.
Accordingly, an object of the present invention is to provide an improved lightweight engine poppet valve constructed in a manner that mechanically attaches the valve head to the stem portion in a locking arrangement with an interfitting joint.
Another object of the present invention is to provide such an engine poppet valve with a valve head made from a titanium intermetallic material that is lightweight, and is durable at optimum temperatures.
Still another object of the present invention is to provide an engine poppet valve manufactured with a valve head attached to a stem portion by means of a compressed interfitting joint.
Still another object of the present invention is to provide an improved method for making a lightweight engine poppet valve that mechanically attaches the valve head to the stem portion in a locking arrangement with an interfitting joint.
These and other objects of the present invention are accomplished with an engine poppet valve comprising a valve head portion, a stem portion, a tip portion and a flared fillet portion of the valve head portion. The flared fillet portion defines a transition region between the valve head portion and the stem portion, and includes an extending portion constructed to form a mechanically locking interfitting joint with the valve stem portion. The valve head portion is made from a lightweight, heat resistant, thermally conductive material.
Another aspect of the present invention is a method for making an engine poppet valve comprising the steps of forming a valve head from a titanium intermetallic material, providing the valve head with a fillet having an extending portion with a preselected length; providing a tubular stem portion, positioning the extending portion of the valve head inside one end of the tubular stem portion; and compressing the tubular stem portion around the extending portion of the valve head for forming a mechanically locking interfitting joint between the extending portion of the valve head and the tubular stem portion.
Still another aspect of the present invention is directed to a method for making an engine poppet valve having a valve head that is durable at high temperatures and thermal resistant, and a deep drawn valve stem portion attached to an extending portion of the valve head with a hydroformed interfitting joint which mechanically attaches and locks the valve head to the stem portion.